What accounts for the essence and unity of Thomism? Two approaches have been developed: a doctrinal approach and a methodological approach, but a third approach has been developed by John of St. Thomas.

Aquinas’ view of substance provides a solution to Descartes’ problem by avoiding a theory of dual substances. Aquinas shows us that we can acknowledge a duality within substance itself, while maintaining its inherent substantial unity.

As the commentary on Isaiah is one of the few which St. Thomas composed on the Old Testament, it is worth taking stock of the manner in which he speaks specifically of Israel and the Jews, even if only briefly.